Morphological changes of the floodplain reach of the Taro River (Northern Italy) in the last two centuries

The quantitative analysis of the planform changes of the unconfined reach of the Taro River, in the Italian Northern Apennines, has allowed the channel evolution in the last 200 years to be outlined. Nine sets of maps and orthophotos, ranging from 1828 to 2011, have been used to evaluate the medium-term changes in channel morphology along the entire time interval, as well as the short-term changes in the most recent decade. Starting from the digitized channel limits and bars, a number of shell scripts based on GIS commands has been used for fast and automatic calculation of the main morphological parameters (channel length, width, braiding, sinuosity, centerline shifting) and for the drawing of graphs showing in detail their continuous variations along the entire study reach. The analysis of the differences in parameters on subsequent dates has revealed that, at least until the end of the 20th century, continuous reduction in channel width (up to a total of 75%) and braiding (43%), as well as continuous increase in channel length (13%) and sinuosity (29%), took place. This is in agreement with most of the previous studies on other rivers, both in Italy and abroad. In contrast with the results of other studies, the most recent evolutionary trend of the Taro River shows substantial morphological stability with possible slight narrowing. The identification of the variations along the channel, facilitated by the analysis of the parameter curves and supported by the historical documentation, reveals that these variations can be substantially attributed to human activities. In particular, the continuous narrowing is largely due to the recurrent subtraction of riverbed areas to be used for agricultural and industrial purposes, as well as to the construction of 10 bridges with the relevant bank protections. The intense mining between 1950s and 1980s seems to have caused a sharp incision and partial narrowing only. The morphological changes due to the reduction in the flow regime, which seem to emerge from the sporadic and discontinuous hydrological data, are expected to be negligible and, in any case, are immaterial when compared with the remarkable changes due to human activities.